In many data processing systems, there is provided between the working memory of the central processing unit and the main memory a high-speed buffer storage unit that is commonly called a “cache”. This unit enables a relatively fast access to a subset of data that were previously transferred from the main storage to the cache, and thus, improves the speed of operation of a data processing system.
U.S. Pat. No. 4,807,110 discloses a prefetching mechanism for a cache and a two-level shadow directory. When an information block is accessed, a parent identifier derived from the block address is stored in a first level of the shadow directory. The address of a subsequently accessed block is stored in the second level of the shadow directory, in a position associated with the first-level position of the respective parent identifier. With each access to an information block, a check is made whether the respective parent identifier is already stored in the first level of the shadow directory. If it is found, then a descendant address from the associated second-level position is used to prefetch an information block to the cache if it is not already resident therein. This mechanism is to reduce the occurrence of cache misses.
U.S. Pat. No. 6,154,767 shows a method and apparatus for using attribute transition probability models for prefetching resources. Idle bandwidth of a client is utilized for the prefetching and resource prefetching by the resource server utilizes idle processing and/or data bus resources of the server.
U.S. Pat. No. 6,151,662 discloses a method of data transaction typing for caching and prefetching. A microprocessor assigns a data transaction type to each instruction. The data transaction type is based upon the encoding of the instruction, and indicates an access mode for memory operations corresponding to the instruction. The access mode may, for example, specify caching and prefetching characteristics for the memory operation. The access mode for each data transaction type is selected to enhance the speed of access by the microprocessor to the data, or to enhance the overall cache and prefetching efficiency of the microprocessor by inhibiting caching and/or prefetching for those memory operations.
From U.S. Pat. No. 6,098,064 a method for prefetching and caching documents according to a probability ranked need list is known. Documents are prefetched and cached on a client computer from servers located on the Internet in accordance with their computed need probability. Those documents with a higher need probability are prefetched and cached before documents with lower need probabilities. The need probability for a document is computed using both a document context factor and a document history factor. The context factor of the need probability of a document is determined by computing the correlation between words in the document and a context of the operating environment. The history factor of the need probability of a document is determined by integrating both how recently the document was used and the frequency of document use.
U.S. Pat. No. 6,154,826 discloses a method for maximizing memory system bandwidth by accessing data in a dynamically determined order. The order in which to access said information is selected based on the location of information stored in the memory. The information is repeatedly accessed from memory and stored in the temporary storage until all streamed information is accessed. The information is stored until required by the data processor. The selection of the order in which to access information maximizes bandwidth and decreases the retrieval time.
Caching is an important technique in all fields of data processing where large amounts of data have to be handled, such as image processing. A particular field of image processing is the rendering, archival, retrieval, processing, transformation, analysis and display of medical images, such as, in the field of digital radiography.
U.S. Pat. No. 6,041,135 shows an interactive off-line processing method for radiographic images. In this off-line image processing method for radiographic images an image is decomposed into detail images and multiple resolution levels and a residual image; detail images are modified up to a preset resolution level and a processed image is reconstructed by means of the modified detail images and the residual image. Interactive processing is performed with different parameter settings.
U.S. Pat. No. 6,127,669 discloses a method for computer aided determination of window and level settings for filmless radiology. Input image data is transformed into an image histogram. This histogram is then segmented into a small number of parts corresponding to structures of interest. Segmentation of the histogram is done by a Viterbi optimal runlength-constrained approximation nonlinear filter.
Window and level settings are calculated to correspond to this segmentation. A readable image of one of the structures of interest is then displayed. In another embodiment, the tool provides a menu of optimal window and level settings corresponding to the different types of information a radiologist may be interested in.
A common disadvantage of prior art workstations for processing and displaying of digital radiographic images is the latency time experiences by the user of the system when a new image is loaded.
This is due to the fact that a single digital radiographic image can be over 50 MB in size. For example, in digital mammography a case to be reviewed by a radiologist is composed of about 4 to 8 different images, each 60 MB in size for certain modalities. A complete case thus is about 500 MB of data.
Even with high-speed processors and memory components such volumes of data result in substantial latency times that are often not acceptable for the users of such workstations. As a consequence, usage of data processing systems for the archiving, transformation, retrieval and transformation of digital radiographic images has been limited so far.